1. Field of the Invention
The present invention relates to an electrical contact for switches, relays, voltage regulators and the like and more particularly to a so-called clad contact comprising a contact segment of a good contact stock such as silver, palladium or the like noble metal, or an alloy thereof and a base segment of copper or its alloy, as a carrier of the contact segment, as well as a method of making same. The contact has an opening therein. A form of the contact may be of a rivet or button.
2. Related Arts
An electrical contact with an opening therein has been proposed, for instance in U.S. Pat. Nos. 2,949,520 and 3,953,698. In the former, the opening is formed in spiral slits extending from a middle part to a rim part of the contact and in the latter, is formed in arc-like slots, which opening serves to guide an arc drawn when contact pieces are separated from each other to keep a contact surface in clear state. However, these contacts have disadvantages in that the spiral slits and a plurality of arc-like slots decrease mechanical strength of the electrical contact per se and a cost thereof becomes higher due to a formation of the slits or slots.
Another type electrical contact has been disclosed in U.S. Pat. No. 3,156,791, wherein an arcuate cross sectional slot is formed in a mating surface of the contact, which promotes the circulation of air to restrain heating and oxidation of the contact. This type contact has also a disadvantages in that it will become difficult to form the slot when a smaller contact is required in use for recent compact and accurate devices.
It has been found that the advantageous functions of the contract as disclosed in said U.S. Pat. No. 3,156,791 can attain by forming an opening in the contact. Therefore, a conventional button type clad contact has been prepared by forming a composite clad plate consisting of a plate of a contact stock such as silver and another plate of a carrier stock such as copper, stamping out from the clad plate discs and then punching out each disc to form a central opening therein. However, this method generates a scrap in large amount, due to the formation of the disc, to reduce a yield of the product in a level of about 30% and further, a recovering of the contact stock from the scrap requires a remarkable time and labour to increase a cost of the final product. While, as far as a conventional rivet type clad contact is concerned, it has been prepared by forming a clad rod with use of the contact stock and carrier stock, as in the button type one, treating the clad rod with use of a header to make the rod into a rivet-like form, and then punching out the formed clad contact to form a central opening or bore therein. In both types of such conventional clad contacts, please note that a hardness of the contat stock and carrier stock is not quite different and thus the punching out for forming the central opening or bore is carried out in the direction from the carrier stock side to the contact stock side, in view of a technical common sense to attain a working accuracy, but this causes a rising up of the carrier stock to a free or top surface of the contact segment formed by the contact stock, at a periphery of the central opening or bore to show a disadvantage of that in use, another contact will contact with the raised carrier portion of the contact to cause in early time period a welding therebetween during switching operations.